Single or multiple electric actuators are frequently arranged in a system and use a method with a microprocessor based controller that controls electrical current supplied to the electric actuator(s) to control extension and retraction of the actuator(s). The term “electric actuator” means electro-hydraulic actuator and/or electro-mechanical actuator. The term “electro-hydraulic actuator” means a self-contained actuator that converts electrical energy to hydraulic energy and applies the hydraulic energy to cause motion. A typical electro-hydraulic actuator, for example, includes an electric motor that drives a hydraulic pump to pressurize fluid from a reservoir and supply the pressurized fluid to a hydraulic cylinder or other hydraulic motor to cause motion. The term “electro-mechanical actuator” means a self-contained actuator that converts electrical energy to mechanical energy to cause motion. A typical electro-mechanical actuator, for example, includes an electric motor that drives a mechanical rod through a mechanism such as a screw thread to cause motion. Such systems and methods are used in a wide range of stationary equipment and mobile equipment. One example of this type of system and method is used with mobile equipment to set and hold a platform for the equipment or other object in a predetermined attitude. The term “attitude” means the orientation or inclination of the axes of the object relative to a plane such as a horizontal plane or vertical plane, and the term “level attitude” means the orientation of the axes of the object in a plane substantially parallel to a horizontal plane.
One example of such system and method used with mobile equipment is a leveling system and method used with motorized or towed recreational vehicles. Generally, when recreational vehicles are to be parked for an extended period of time, a set of leveling electric actuators are utilized to level and support the vehicle. The most common types of leveling electric actuators, which are most commonly installed by the recreational vehicle manufacturer, are of a scissor type or telescoping type. Typically, such leveling electric actuators are used at both the front and the rear of the recreational vehicle and are extended to level the vehicle. The leveling electric actuators attach, often permanently, to the frame of the recreational vehicle to support the vehicle above the ground or other surface on which the recreational vehicle is parked.
Once the recreational vehicle is driven to the location where it will be parked, such as for example a campground or sporting event, the leveling electric actuators are engaged to raise the recreational vehicle, to take much of the weight off of the vehicle's tires and to support the vehicle in a generally level attitude. Sometimes the electric actuators may be extended individually and then checked and reset to obtain a proper level attitude.
In control systems and methods used with single or multiple electric actuators, a technical problem is presented if only some of the electric actuators carry a substantial part of the load. For example, recreational vehicle or other object leveling systems that use multiple electric actuators to position the vehicle or other object in a level attitude can level the object with only some of the actuators carrying a substantial part of the total object weight or load. This may occur, for example, if one side of the recreation vehicle is lower relative to ground than the other side of the vehicle. In this example, the electric actuators on the lower side may be extended to lift the lower side and achieve a level attitude for the vehicle while the actuators on the higher side are not carrying the proper part of the total vehicle weight or load. If this occurs, the tires on the high side of the vehicle and possible even the tires on the low side of the vehicle may carry a greater part of the weight than desired. If the tires carry too much of the weight when the vehicle is parked, even if the vehicle is in a level attitude, the vehicle may sway in a side-by-side direction or shift in a front-to-back direction due to the movement of occupants inside the vehicle or due to wind or other causes. To address this problem, some prior art recreational vehicle leveling systems may use a central hydraulic pump that supplies hydraulic fluid to multiple hydraulic actuators attached to the frame of the vehicle, with a pressure sensor to indicate a hydraulic pressure level in all of the actuators that indicates all of the actuators are carrying a substantial part of the load before leveling the vehicle is completed. Other prior art systems are disclosed in U.S. Pat. No. 5,143,386. These systems sense ground contact using a Hall effect current sensor and bring the actuators to a stop when each is lifting a minimum load and the vehicle has reached a level position.
It is desirable in single or multiple electric actuator control systems and methods to sense the load carried by the actuator(s) and provide an extending or retracting electrical current to the actuator(s) that achieves preselected load requirements. Further, in such systems and methods, it is desirable to sense the load carried by the actuator(s) and extend or retract the actuator(s) after a preselected minimum load is achieved to achieve a further objective such as positioning an object in a level attitude. Still further, in such systems and methods, it is desirable to have the ability to relatively easily increase or decrease the number of electric actuators provided so that the system can be used in a wide variety of applications.
It would be desirable to provide such a system and method in which an abrupt change in the velocity of movement of the actuator, such as for example by action of the operator or by the actuator starting or reaching the end of its stroke or encountering an abrupt increased resistance to its movement, would not cause objectionable erratic movement or jerking. Further, it would be desirable to provide such a system and method that would operate satisfactorily over a wide range of temperature conditions. Further, it would be desirable to provide such a system and method in which precise synchronization or tuning of the system for transient conditions would not be required to minimize such erratic movement or jerking. Still further, it would be desirable to provide such a system hick hydraulic motor position sensors or load or pressure sensors to measure the actuator condition would not be required.